1. Field of the Invention
The present invention relates to a line accommodation device, a control method and a control program thereof, and more particularly relates to a technology effective when applying them to a line accommodation technology for collecting a plurality of communication system stations and communication nodes or the like.
2. Description of the Related Art
In order to stably transmit/receive frames in many data network, networks utilizing a failure relief function possessed by a communication system, such as a synchronous optical network (SONET), a synchronous digital hierarchy (SDH), a wavelength division multiplexing (WDM) and the like are designed. In such a situation, a rating for realizing a failure relief function at a frame level while using SONET as a communication medium is the resilient packet ring (RPR). Thanks to the RPR rating, there becomes no need to build a redundancy configuration in order to relieve failures in SONET, SDH and WDM.
However, SONET or the like is still used as a communication medium, a network, such as SONET or the like must be built before an RPR is used.
As the prior art, there is IEEE 802.17 (RPR rating). In this rating, the detailed building method of an RPR network is not especially referred to. As indicated in the rating, in an RPR, it is important for RPR stations (hereinafter called “station”) are connected via two ring-shaped information transmission lines (ringlet) for transmitting information in mutually opposite directions. However, no attention is paid to how the stations are connected when SONET is used as a communication medium.
Judging from the disclosed contents of the rating, each station comprises one set of SONET interfaces (the combination of a clockwise SONET interface (SO1) and a counter-clockwise SONET interface (SO2)). If a station comprises a SONET interface, it is anticipated that a plurality of stations or a plurality of SONET interfaces is added/deleted to/from a line accommodation device accommodating the station (hereinafter called “shelf”). However, the configuration modification caused in such a shelf is not referred to.
Generally, a communication device capable of providing a large capacity of line services, such as a router, a transmission device or the like adopts a shelf structure. In this case, it is preferable to embody each communication service (such as a station, a SONET interface, etc,) in the form of a card (substrate) and to be able to freely insert/remove this card in/from the shelf.
If the RPR function is applied for such a usage, the contents disclosed of the above-mentioned rating is incomplete as it is. Particularly, a network must be built paying attention to the following points.    (1) Disposing stations in a ring shape    (2) Connecting a SONET interface in such a way not as to avoid wrong the East/West directions for a ring    (3) Carefully connecting an optical fiber to a target ring if a plurality of RPRs is collected in the shelf
These setting (1) through (3) must be made for each station. As the combination of stations, not only the combination of stations in a shelf but also the combination of stations across a plurality of shelves are anticipated. In any case, attention must be paid so as to avoid a wrong connection.
In the RPR rating, the following alarms are issued if there is a wrong connection.    (1) Mis-cable    (2) Mis-cable connection    (3) Keep-alive timeout    (4) A regular report cannot be received from an adjacent stationHowever, these are not caused as long as there is no hardware failure, such as the wrong connection of east/west cables, a station failure or the like. Therefore, a method for detecting that a station is connected to an unintended RPR is not defined.
As to the failure relief of an RPR, if a station fails, it is clearly specified in the rating that the station should be disconnected. As the removal method, the steering/wrapping of the RPR is simply used. Therefore, when the station is broken and when the layer of a SONET, a SDH and a WDM fails, they are similarly relieved. In other words, even when a station is broken, the steering/wrapping of an RPR occurs.
Therefore, a network in which the RPR steering/wrapping occurs due to the failure of a station cannot activate a new RPR steering/wrapping until the station recovers from the failure. During this period, redundancy continues to be lost. In an RPR in which the length of one ring is assumed to be 2,000 km, there is a possibility that stations may be scattered a long distance away from each other. Therefore, it is not easy to switch the broken station. In this case, it takes a long time to recover the redundancy, that is, reliability of the station.
The above-mentioned problems of the prior art can be summarized as follows.    (1) The addition of a station to an arbitrary ring is not assured.    (2) The deletion of a station from an arbitrary ring is not assured.    (3) The connection of stations to the same ring across a plurality of shelves is not assured.    (4) When a station is broken, the station can be disconnected from the ring by RPR steering/wrapping. However, if another failure occurs by the influence, failure relief by RPR steering/wrapping cannot be realized.
Patent reference 1 discloses a transmission device for independently performing ring switching at a SONET/SDH network level and ring switching at a network level, such as an RPR or the like by providing a network signal processing means for switching a ring for each network signal using a synchronous signal obtained from a connection means connected to the SONET/SDH network. However, it does not recognize the above-mentioned technical problem in the case where a plurality of stations or SONET interfaces is installed in one shelf.    Patent reference 1: Japanese Patent Application No. 2004-23620